scala - Scala 中的链式比较

Question

Python 支持“链式比较”的优雅语法，例如:

0 <= n < 256

意思，

0 <= n and n < 256

知道它在语法上是一种相当灵活的语言，是否可以在 Scala 中模拟此功能？

Answer 1

Daniel的回答很全面，实际上很难添加任何内容。由于他的回答提出了他提到的其中一个选择，我只想补充我的 2 美分，并以另一种方式提出一个非常简短的解决方案。丹尼尔的描述:

You could, theoretically, feed the result of the one of the methods to another method. I can think of two ways of doing that:

• Having <= return an object that has both the parameter it received and the result of the comparision, and having < use both these values as appropriate.

CmpChain 将用作已与最右边的自由对象进行比较的累加器，以便我们可以将其与下一个进行比较:

class CmpChain[T <% Ordered[T]](val left: Boolean, x: T) {
  def <(y: T) = new CmpChain(left && x < y, y)
  def <=(y: T) = new CmpChain(left && x <= y, y)
  // > and >= are analogous

  def asBoolean = left
}

implicit def ordToCmpChain[T <% Ordered[T]](x: T) = new AnyRef {
  def cmp = new CmpChain(true, x)
}
implicit def rToBoolean[T](cc: CmpChain[T]): Boolean = cc.asBoolean

您可以将其用于任何有序类型，例如 Int 或 Double:

scala> (1.cmp < 2 < 3 <= 3 < 5).asBoolean                          
res0: Boolean = true

scala> (1.0.cmp < 2).asBoolean
res1: Boolean = true

scala> (2.0.cmp < 2).asBoolean
res2: Boolean = false

隐式转换将产生 Boolean ，它应该是:

scala> val b: Boolean = 1.cmp < 2 < 3 < 3 <= 10  
b: Boolean = false